1. Field of the Invention
The present invention relates to a cylindrical roller bearing for use in a general machine such as a middle-size electric motor, a large-size electric motor, or the like. Particularly, the present invention relates to an improvement of a cylindrical roller bearing for use in an apparatus requiring both low vibration and low noise.
2. Description of the Related Art
As a technique for reducing both vibration and noise of a cylindrical roller bearing, heretofore, there is a technique in which the contact position between each rolling element and a cage varies in accordance with difference in the guiding method (race guiding or rolling element guiding) of the cage as described, for example, in Japanese Utility Model Publication No. Hei. 3-67718, or a technique in which the contact form is changed as described, for example, in Japanese Patent Publication No. Hei. 7-127645.
Further, in the cage described in Japanese Utility Model Publication No. Hei. 3-67718, particularly the motion of each rolling element in an unloading range is limited to thereby attain the reduction of both vibration and noise of the bearing. That is, since the guiding method of this cage is of the rolling element guiding type, the weight of the cage is loaded on each rolling element in the unloading range. The load becomes a counter force to a centrifugal force acting on the rolling element when the bearing is rotating. Accordingly, the contact pressure between the rolling element in the unloading range and an outer race is reduced. As a result, the vibration of the bearing is suppressed.
Here, in a press cage, it is general that a roller guide surface of the cage is provided from a neighbor of an annular portion and formed in a crowning portion of a rolling surface of each roller as described, for example, in Japanese Utility Model Publication No. Hei. 6-87723, or the like.
In the bearing described in Japanese Utility Model Publication No. Hei. 3-67718, however, as shown in FIG. 10, the pitch circle diameter of each pocket 50a of the cage 50 is set to be smaller than the pitch circle diameter of each roller 51. Accordingly, if the bearing is produced so that the difference between the two pitch circle diameters is not made proper, the limitation given by the cage 50 to the roller 51 becomes severe. When the limitation was too severe, the roller 51 and the cage 50 interfered with each other more intensively than necessary so that noise of collision was often produced between the cage 50 and the roller 51 (cage noise).
Further, when the limitation of the cage 50 was severe, the vibration and noise levels of the bearing often varied because the bearing was easily affected by error in individual production of the cage 50.
Further, since the guiding method was limited to the rolling element guiding type, the specifications of the bearing were often limited inevitably.
Incidentally, in the conventional cylindrical roller bearing, the whole contour of a rolling surface of each roller 51 along the direction of an axis of the roller was generally shaped like a composite circular arc crown (partial crowning shape) having a linear portion and a curved portion or like a curved full crown in order to relax edge loading. Accordingly, each roller 51 moving in the unloading range was pressed against a surface (pillar-side surface) of the pocket 50a of the cage 50 facing the roller 51 in the circumferential direction by point contact. The axis of the roller 51 varied easily regardless of presence/absence of inclinations of the pillar-side surface of the pocket 50a with respect to the circumferential and radial directions, so that there was no function to allow the roller 50 to take a stable posture.